1. Field of the Invention
This invention relates to a method for producing polysilazane which can be a precursor for silicon nitride dominating ceramics.
2. Description of the Prior Art
Since a so-called precursor method in which heat-resisting ceramics are produced by pyrolysis of organometallic polymers, has the advantages such as capability of forming products of special shapes which have not been obtained through conventional processings of ceramics powder, easy attainment of products having purity higher than those obtained through conventional processes, capability of being processed at a lower temperature or the like, research works thereof are becoming active. As one of them, there is a method in which polycarbosilazanes are subjected to pyrolysis to obtain ceramics containing, as its principal component, silicon nitride. For example, in the publication of Japanese examined patent application No. 46995 of 1980 (as well as in FR. No. 2,190,764, U.S. Pat. No. 3,853,567 and DE No. 2,218,960), there is described a methord in which tris(methylamino)methylsilane which is obtained by causing methyltrichlorosilane to react with methylamine, is subjected to heat treatment at about 520.degree. C. to obtain polycarbosilazane. Resultant polycarbosilazane is subjected to pyrolysis to obtain ceramics. However, in case of the abovementioned method, since there are a large amount of organic residual groups included in the formed polymer, the loss during pyrolysis is so large as about 35.about.45% and since a considerable amount of carbon is remaining in ultimate ceramics, (content of Si.sub.3 N is about 50%), it is not a preferable material as a precursor polymer for obtaining a high purity silicon nitride. Further, a higher temperature necessary for obtaining a polymer such as 520.degree. C. is not preferable from the view point of energy-cost.